the triggering probability of radio‐ loud agnrieth/talks/hergs_and_lergs.pdf · conclusions...
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The triggering probability of radio‐
loud AGN
October 10, 2012 Henry Cornell
Dave Riethmiller
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AcCve GalacCc Nuclei: DefiniCon • Compact region at the center
of a galaxy
• Very high luminosity over some porCon (or all porCons) of the EM spectrum
• RadiaCon caused by accreCon of mass by supermassive black hole
• Quasars, Blazars, Radio Galaxies
• Radio Loud or Quiet
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Brightest type of radio loud classified as “Radio galaxy.”
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Radio Galaxies • Produce large jets and lobes
• Lobe emission from synchrotron radiaCon
• Associated with recently merged ellipCcal galaxies
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HERGs (High‐ExcitaCon Radio Galaxy)
Gas from cold reservoir reaches SMBH, accreCon at higher rates in radiaCvely efficient process, AGN has many luminous emission lines.
LERGs (Low‐ExcitaCon Radio Galaxy)
Hot gas from red ellipCcal’s X‐ray halo falls at low Eddington rates onto SMBH’s center. RadiaCvely inefficient accreCon process, AGN lacks luminous emission lines.
Advec-on‐Dominated Accre-on Flow Important for accreCon rates well below the Eddington limit. AccreCng ma]er does not form a thin disc and consequently does not radiate away the energy that it has acquired in moving close to the black hole.
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The Sample VASC database constructed from SDSS, NVSS, FIRST cross comparisons. For each galaxy, VASC contains derived quanCCes
stellar mass M* star formaCon rate SFR VASC
value‐added spectroscopic catalogs SDSS Sloan Digital Sky Survey NVSS NaConal Radio Astronomy Observatory (NRAO) Very Long Array (VLA) Sky Survey FIRST Faint Images of the Radio Sky Telescope at twenty cenCmeters
927,522 galaxies in VASC 18,286 idenCfied as radio sources
RL source radio emission Ced to star formaCon
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Dn(4000)
RaCo of shaded regions termed “4000‐A break strength.”
If galaxy with recent star formaCon (i.e. young blue stars), will see more blue light from new stars.
red blue
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The Sample VASC Radio Sources
+ Radio emission Ced to star formaCon
Radio‐Loud Source
Best et al., 2005
HERGs LERGs
filter based on redshih, filter based on mass, throw out QSOs...
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High vs Low ExcitaCon
Best et al., 2012 ClassificaCon scheme based on strengths of 6 line raCos: [O III] 5007/Hα [O III] 5007/[O II] 3727 [O III]/Hβ [N II]/Hα [S II]/Hα [O I]/Hα and a set of classificaCon rules
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What Color? # galaxies per bin
Orange: Strateva et al. 2001
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Radio‐Loud AGN in the local universe are dominated by LERGs.
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Radio‐Loud AGN FracCon
InvesCgate which galaxies preferenCally host RL AGN by determining the fracCon fRL as funcCon of: host galaxy mass star formaCon rate color (x) radio luminosity & excitaCon (y) A = all RL AGNs G = all galaxies V = volume in which each galaxy can be observed
fRLy,x
=1
Vmax
ii! Ay ,x
#
%
&
(
1
Vmax
jj ! Gy ,x
#
%
&
(
) 1
fRLy,x
= N y,xA / N
xG
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1. AGN ExcitaCon & Host Mass
fRLLE
!M*
2.5
fRLHE
!M*
1.5
LERG dependence saturates at ~11.6 M* HERGs much less dependent on radio luminosity cut.
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2. Host Mass & SFR
log fRL LERG fRL bands horizontal, no correlaCon. HERG fRL bands show preferenCal direcCon.
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3. Color & Host Mass LERGs: Red and Green fracCon drops strongly with luminosity cut, Blue mostly unchanged.
HERGs show preference for blue or green galaxies, over red.
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4. Color & Luminosity
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5. Color & SFR
Blue populaCon (HERGs and LERGs) shows steep dependence on SFR, Green not so much. Luminosity cut differences also apparent. Red fracCon higher in LERGs than HERGs.
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Conclusions Radio‐Loud AGN in the local universe are dominated by LERGs, as is
evident by the LERGs’ stronger mass dependence, regardless of color: The probability that a red galaxy hosts a LERG depends strongly on the
applied radio luminosity cut.
The probability that a green galaxy of a given mass hosts a LERG is lower compared to both red and blue populaCon.
The probability to host a HERG is significantly higher in green or blue than in red galaxies.
Within the blue populaCon, the probability to host a RL AGN (both HERG & LERG) is strongly correlated with SFR. This dependence is weaker or absent in red or green populaCons.
fRLLE
!M*
2.5fRLHE
!M*
1.5
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Conclusions
Results suggest that presence of cold gas in a galaxy enhances probability that its SMBH becomes luminous RL AGN, compared with the typical LERG model in red ellipCcals.
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HERGs (High‐ExcitaCon Radio Galaxy)
Gers frerm cerld rerservoir rerches SMBH, accrerCon at higher rertes in rerdiaCvely effercient prercess, AGN has merny lerminous emerssion lernes.
LERGs (Low‐ExcitaCon Radio Galaxy)
Hert gers frerm rerd ellerpCcal’s X‐ray herlo ferlls at lerw Eddington rertes onter SMBH’s cernter. RerdiaCvely ineffercient accrerCon prercess, AGN lercks lerminous emerssion lernes.
Admit it ‐ you’ve been thinking this through the whole talk:
ERMERGERD
LERGS